At the start of this incredible novella, it is clear that Kino and Juana enjoy a very close and intimate marriage. Note, for example, the description we are given of the family unity which they enjoy, in spite of their poverty and need:
Juana sang softly an ancient song that had only three notes and yet endless variety of interval. And this was part of the family song too. It was all part. Sometimes it rose to an aching chord that caught the throat, saying this is safety, this is warmth, this is the Whole.
The images of domestic harmony and unity that the first chapter gives us as both Kino and Juana carry on their roles in a way that speaks of an intimate relationship are changed however as the pearl enters their lives and Kino becomes more obsessed by it. We are shown that their marital harmony is disrupted by this evil force, and the impact that the pearl has on it. You might want to consider the way that Kino reacts when he catches Juana trying to return the pearl to the sea.